This invention relates to an apparatus for providing a stream of fresh air to an enclosed space, and more particularly, to an apparatus for providing a stream of cooled or heated fresh air to an enclosed space.
Air to air heat exchangers are becoming increasingly important to reduce the cost of cooling or heating air supply fed to an enclosed se such as a building. Such heat exchangers are required to handle relatively high air-flow rates (often in the range of 500 to 5000 liters per second) and to transfer heat with relatively high thermal efficiency between the two mutually-isolated air flow circuits of the heat exchanger. Fresh air is supplied to the enclosed space through one of these circuits while simultaneously stale air is withdrawn from the space and is conveyed through the other circuit.
It is customary to maintain a slight positive pressure in the enclosed space to prevent ambient air at a different temperature to that desired, entering the enclosed space when an access door is temporarily opened. However the rate of air flow through the two circuits is conventionally of much the same order to achieve total air replacement, as it only requires a slightly greater flow of the air into the confined space to maintain the slight increase in air pressure within it.
It is an object of the present invention to o e or ameliorate at least one of the disadvantages of the prior art or to provide a useful alternative
The present invention provides an apparatus for supplying a stream of fresh air to an enclosed space whilst simultaneously withdrawing a stream of stale air from the space said apparatus having a heat exchanger with mutually isolated primary and secondary air flow circuits and adapted to provide heat transfer between said primary and secondary air flow circuits, with one of the circuits connected to receive a steam of fresh and the other circuit connected to receive a stream of stale air at a different temperature from that of the fresh air stream; the apparatus further including a refrigeration circuit having two separate hear exchange units which are respectively arranged at the air outlets of the two air flow circuits.
Advantageously, the present invention provides for an improvement in the thermal efficiency of an air flow heat exchanger having isolated and primary and secondary circuits between which good heat-transfer characteristics occur and forming part of apparatus for providing a stream of fresh to an enclosed at a desired temperature
The invention is especially, although not exclusively, useful in conjunction with a reverse cycle refrigeration unit and/or direct/indirect gas-fired heating as is disclosed in my co-pending International Patent Application No. PCTJ/AU998/00559 entitled xe2x80x9cDirect/Indirect Gas Heating of Airxe2x80x9d.
The refrigeration circuit is preferably of a closed come on circuit type. The invention may be used for cooling a steam of fresh air supplied to the space, in which case the hear exchange unit of the refrigeration circuit at the air outlet acts as a coding evaporator and, the second heat exchange unit of the refrigeration circuit acts as a hot condenser which is cooled by the stream of stale leaving the heat exchanger. The invention is also uscable with a reverse-cycle compression refrigeration circuit, in which case the two heat exchange units are each capable of act either as a cooling evaporator or as a hot condenser.
An advantage of the invention is that when the apparatus is operating in a cooling mode so as to provide a stream of cooled fresh air to an enclosed space The thermal efficiency of he closed compression refrigeration circuit is substantially improved as the rate of removal of heat from the hot condenser of tie refrigeration circuit by the stale air strum is greatly increased.
When the apparatus is required to pride tie space with a stream of cool fresh air, the heat-absorbing capacity of the stale air stream is suitably enhanced by cooling and increasing its humidity before it enters the heat exchanger. This may be achieved by means of water sprays. However the preferred way of cooling the stale air stream and increasing its humidity is by passing the stale air stream through a water moistened evaporative cooling pad, such as a CELdek(trademark). A CELdek(trademark) cooling pad provides a multi-channel structure having a large number of air-flow channels extending between its opposite faces. Water is pressed over its surfaces exposed to the stale air stream, typically under the effect of gravity. The air stream absorbs moisture vapor from the cooling pad which in turn is cooled by the absorption of the latent heat of vaporization from the water down through it. The cooling of the pad in this manner cools the stale air stream flowing through it before it enters the heat exchanger and the fresh air streamer is cooled to a lower temperature in the heat exchanger as a consequence.
An apparatus for supplying cooled to an enclosed space is described in detail in my co-pending International Patent Application No PCT/AU95/00315, WO 95/33960 hereby inserted by way of reference.